CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY OF THE MUSEUM 

 OF COMPARATIVE ZOOLOGY AT HARVARD COLLEGE. E. L. MARK, 



Director. No. 193 



THE REACTIONS OF PLANARIANS TO LIGHT 



BY 



HERBERT EUGENE WALTER- 



With Fourteen Figures 



I Introduction 37 



II Historical 3^ 



III Material '. 45 



IV Criteria for measuring behavior 47 



V Observations 49 



1 Photokinesis 49 



A Behavior in dark 50 



Rate of locomotion 50 



Turning 5' 



Change of course 51 



Summary 5' 



B Non-directive light 52 



a Apparatus 5^ 



b Results 56 



Rate of locomotion 56 



Turning 5^ 



Changeof course 59 



Degree of wandering 60 



Interval of response 60 



Manner of coming to rest 6i 



Summary 62 



C Abrupt changes of light intensity 62 



a In time 63 



b In space 64 



Summary 71 



2 Phototaxis 7^ 



A In constant directive light 72 



Orientation 7^ 



Rate of locomotion 75 



Change in character of course 78 



Accuracy of orientation 79 



Degree of wandering 80 



Duration of activity 81 



Time required to leave a unit circle 82 



Manner of coming to rest 83 



Summary 86 



Journal or Experimental Zoology, vol. v, no. i. 



